A vehicular braking apparatus that executes ABS control using a pressure regulating reservoir (switch reservoir) is disclosed in Japanese Patent Laid-Open Publication No. 2000-142346. The pressure regulating reservoir illustrated by Japanese Patent Laid-Open Publication No. 2000-142346 will be described with reference to FIG. 11.
FIG. 11 is a cross sectional view showing a cross section of the pressure regulating reservoir. As shown in the figure, the pressure regulating reservoir has a structure including a hollow portion that forms a reservoir chamber J2 in a housing J1 forming a brake conduit. The following are included inside the hollow portion: a ball valve J3, a valve seat J4, a filter component J5, a piston J6 with a shaft J7 fixed thereto, a spring J8, and a stopper J9.
The ball valve J3, the valve seat J4, and the filter component J5 are formed as a unit, such that the ball valve J3 is mounted on the filter component J5 and the valve seat J4, when the filter component J5 and the valve seat J4 are fixed. Disposed inside the filter component J5 is the spring J10, which biases the ball valve J3 towards a side of the valve seat J4.
The piston J6 is structured so as to be capable of sliding against an inner wall of the hollow portion of the housing J1 forming the reservoir chamber J2. Designated as top dead center is a stepped portion formed by a wall of the hollow portion of the housing J1 forming the reservoir chamber J2. Furthermore, a step or groove (not shown) is provided on an upper surface of the piston J6 so that the entire surface of the piston J6 does not contact the housing J1 when the piston J6 and the housing J1 come in abutment. The purpose of this is to facilitate the flow of brake fluid from an suction hole to a discharge hole.
The piston J6 slides against an inner wall of the hollow portion of the housing J1 forming the reservoir chamber J2. When this occurs, there is considerable slide resistance if both the housing J1 and the piston J6 are metal, for which a countermeasure is required to lower the slide resistance. However, the slide resistance becomes small in the case of a resin piston J6, making the countermeasure to lower slide resistance unnecessary. Thus, the piston J6 is provided with a wear ring J11 made from resin to facilitate sliding against the inner wall of the metal housing J1, and is also provided with an O-ring J12 that functions as a seal.
The shaft J7 is press-fit into a concave portion formed at a central position of the piston J6. The shaft J7 is also structured such that an end of the shaft J7 contacts the ball valve J3 via a hole in the valve seat J4 when the piston J6 is accommodated in the hollow portion of the housing J1 forming the reservoir chamber J2.
Also formed on the housing J1 are two passages J13, J14 that communicate with the reservoir chamber J2. In the passage J13, the unit comprising the ball valve J3, the valve seat J4, and the filter component J5 are caulked and fixed thereto.
In the pressure regulating reservoir structured as described above, during normal braking the piston J6 is pressed upward in the cross section of FIG. 11 by the elasticity force of the spring J8. This in turn causes an end of the shaft J7 to move the ball valve J3 away from the seat of the valve seat J4. When brake fluid is then supplied via the passage J13, the brake fluid thus accumulates in the reservoir chamber J2 via the hole in the valve seat J4. The accumulated brake fluid in the reservoir chamber J2 is sucked up by a pump (not shown) via the passage J14 and then supplied to wheel cylinders (hereinafter as referred to W/Cs, not shown).
After a predetermined amount of brake fluid has accumulated in the reservoir chamber J2; and a slide amount of the piston J6 has become greater than an offset amount between the ball valve J3 and the valve seat J4, i.e., a lift amount of the ball valve J3, the ball valve J3 contacts the seat of the valve seat J4 again. Accordingly, the passage J13 is closed, and the brake fluid flow into the reservoir chamber J2 via the passage J13 is regulated. In this manner, brake fluid is prevented from flowing into the reservoir chamber J2 until the piston J6 reaches bottom dead center. Furthermore, high-pressure brake fluid farther upstream than the pressure regulating reservoir (on the passage J13 side) is not supplied as is downstream (to the passage J14 side).
In the above-described pressure regulating reservoir, the lift amount of the ball valve J3 is controlled to regulate the flow of brake fluid into the reservoir chamber J2. In other words, the lift amount of the ball valve J3 is determined by the positional relationship of the ball valve J3 and the end of the shaft J7. Therefore, the positional relationship of the ball valve J3 and the end of the shaft J7 is controlled.
However, assembly errors may occur when integrating the shaft J7 into the piston J6, or when assembling the unit including the ball valve J3, the valve seat J4 and the filter component J5 to the passage J13. The effects of these assembly errors, as well as variations in the dimensional accuracy of each component, often make it difficult to achieve the above control.